| dc.description.abstract | This work monitored short-term variations of water-soluble inorganic ions (WSIIs) of atmospheric PM2.5 using Particle-Into-Liquid-Sampler coupled with an Ion Chromatograph (PILS-IC) at the Lulin Atmospheric Background Station (LABS, 2,862 m a.s.l.) in spring 2014. In addition, PM2.5 and PM10 mass concentrations, PM10 and PM1.0 scattering and absorption coefficients, aerosol size spectra, aerosol total number concentration, and dynamic variations of gaseous pollutants were also monitored at LABS.
Under prevailing westerly, LABS is a proper site for observing transported biomass burning (BB) smoke and Asian continent pollution due to its downstream location of the air masses transported from Southeast Asia. In this study, short-term dynamic variations of WSIIs were observed during different pollution events. Meanwhile, formations of WSIIs from dissolved atmospheric SO2 and NH3 in fog were evaluated to investigate dynamic variations of WSIIs in inactivated aerosol and fog droplets during fog.
All pollutant levels were very low when backward trajectories were originated from free atmosphere. The concentrations of NH4+, NO3-, SO42, and K+ were 0.1 ± 0.4, 0.2 ± 0.4, 0.7 ± 0.7, and 0.0 ± 0.0 μg m-3, respectively, which may represent clean atmospheric background of East Asia during extensive BB period. In contrast, CO, PM2.5 mass level, PM1 green scattering and absorption coefficients were all enhanced when affected by the transported BB smoke. The corresponding concentrations of NH4+, NO3-, SO42, and K+ were 1.9 ± 1.5, 1.0 ± 1.0, 3.6 ± 2.9, and 0.2 ± 0.2 μg m-3, respectively. From linear correlation analyses of these chemical components, ammonium sulfate and ammonium nitrate are their possible compound forms.
The levels of CO, NOx, NH4+, SO42-, and NO3- were observed to increase with time during fog event periods at LABS. It suggests that ground-level pollutants were transported by the uplift flow to form fog at LABS. Moderately high linear correlation between SO42- and NH4+ (R2>0.64) indicated that the compound form of these two ions might be ammonium sulfate or ammonium bisulfate. From the calculation of ExNO3- and ExNH4+, three nitrate formation pathways (Mwaniki, et al., 2014) can be inferred to be condensed HNO3(g) onto aerosol surface, N2O5 hydrolysis, or the formation of ammonium nitrate particles in different times. Moreover, the modal diameter of aerosol size spectra was gradually increased in the fog events which showed a coagulation growth of aerosol in the fog.
A value of DIGMI (Dissolved Gas over Measured Ions) was calculated from measured SO42- and NH4+ concentrations by PILS-IC and the dissolved SO42- and NH4+ concentrations in fog droplets in equilibrium with atmospheric SO2 and NH3. The DIGMI values of SO2 were mostly close to 1.0 during normal fog events indicating good gas dissolution. However, the DIGIMI values varied greatly when affected by the transported BB smoke. For NH3, the mean DIGIMI values were both greater than 1.0 with/without an effect of the transported BB smoke implying a good dissolution of NH3 in fog droplets. | en_US |